Pressurized containers are well known in which the product and the propellant are intermixed, dissolved, or dispersed, such containers being often or usually referred to as aerosol containers. After actuating the valve, the product and the propellant exit together.
It is also generally known that pressurized containers can be constructed as two-compartment spraying systems in order to avoid having the product come into contact with the vessel and/or the propellant. In this way it is possible to fill aggressive and pasty products into metallic vessels such as tinplate containers, and release the product as a spray, foam, or squeezed paste without intermixing with the propellant.
In two-compartment spray systems metal or glass vessels are used as outer containers, as they have been used for several decades as aerosol containers for filling with materials such as body care products, hair care products, insecticides, impregnating sprays, technical aerosols, etc. The liners which serve for the acceptance of the products which have to be released, are bags made of flexible material like, for example, thermoplastic synthetic material or aluminum. The bag, which is affected by the pressure of the propellant, is gradually compressed when the pressure in the liner is released and when the product is transported out of the opening of the valve of the pressurized container in the form of a spray, a foam, or a squeezed paste after the valve has been actuated.
As a propellant all types of compressed gases such as, preferably, environmentally safe compressed air, and also condensable gases can be used.
All these generally known two-compartment spray systems have in common a disadvantage that, on the bottom of the pressure resistant vessel, an additional small opening is required. The flexible liner is suspended in the container by being pinched at the brim of the opening of the vessel during the crimping process. In order to obtain clearance for the wall thickness of the liner in the area of its opening, the opening of the aerosol containers must be enlarged to be wider than the standard opening diameter.
The filling process is done in such a way that, firstly, the product is filled into the empty liner which previously had been inserted into the vessel; then the filled liner equipped with a valve is connected to the vessel by clinching. With special equipment the propellant is inserted by way of the small hole at the bottom. Then, the bottom hole is closed by means of an elastic bung. Now the necessary spray actuator or paste squeezing spout is mounted upon the valve which is combined with the vessel. By actuating the valve the product streams out of the vessel under the power of the pressurizing medium upon the liner.
Since the propellants which until recently were commonly used in aerosol containers, namely fluorochlorohydrocarbons, were thought to be harmful to the ozone layer of the globe, there has been an increasing interest to replace these propellants by less dangerous condensible gases or abandon all types of such propellants. The two-compartment spray systems, in which compressed air is the pressurizing agent and, in consequence, a propellant, are considered to be a good alternative. However, this system involves several disadvantages. The elastic bung which is inserted in the bottom hole tends to cause the loss of pressure during extended periods of storage because of the inadequate sealing resulting from the irregular shape of the hole and/or the deterioration of the bung material, as a result of which the function of the vessel is partially or completely impaired. The enlarging of the opening of the vessel and the creation of the bottom hole can be imprecise, so that the irregular deformation during the process of enlarging the diameter of the opening, and the perforation of the bottom cannot be avoided. In addition, containers which are modified in this way do not comply with the original design which has been approved by the authorities. Furthermore, the process of filling these containers is time consuming, complicated, and expensive.